Cooperative diversity has recently received wide recognition as a simple way to improve system error rate performance and capacity by forming virtual antenna arrays. For amplify-and-forward (AF) cooperative or relay networks, a number of distributed space-time (ST) coding schemes have been developed. Most of these coding schemes can achieve the maximum cooperative diversity gain in cooperative networks but at the cost of reduced symbol rate.
A non-orthogonal AF (NAF) scheme was proposed by allowing the source to continue transmission over the whole duration of the cooperation frame while the cooperative partner listens and relays. The NAF scheme was later proved to achieve the optimal diversity-multiplexing tradeoff (DMT) for the single-relay scenario. However, it is desirable to achieve optimal diversity multiplexing for multiple relays.
For the general case of arbitrary number of relay nodes, the best known DMT has been recently presented with a so-called naive slotted AF cooperative scheme. To realize a high symbol rate while guaranteeing full diversity, a few coding schemes were proposed. Based on one-by-one relay transmission, some existing optimal ST codes were applied to half-duplex NAF channels. However, one-by one relay transmissions reduces the symbol rate that can be transmitted.
The above-described deficiencies of cooperative wireless network communications are merely intended to provide an overview of some of the problems of today's cooperative wireless networks, and are not intended to be exhaustive. Other problems with the state of the art may become further apparent upon review of the description of various non-limiting embodiments that follows.